Direct view storage tube erasure



March 10, 1964 G. w. KING ETAL 3,124,717

DIRECT VIEW STORAGE TUBE ERASURE CIRCUIT Filed Dec. 23. 1960 2Sheets-Sheet 1 INVENTOR. GEORGE W. KING WALTER E. SALLSTROM BY JAMES L.FOY

March 10, 1964 G. w. KING ETAL 3,124,717

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United States Patent 3,124,717 DIRECT VIEW STORAGE TUBE ERASURE CIRCUITGeorge W. King, Pleasantville, and Walter E. Sallstrom, Croton Falls,N.Y., and James L. Foy, Gardena, Calif., assignors to General Precision,Inc., a corporation of Delaware Filed Dec. 23, 1960, Ser. No. 77,918 7Claims. (Cl. 315-14) This invention relates to direct view storage tubesand more particularly to a method and a means for controlling erasure ofthe image stored within the tube.

Direct view storage tubes are comparatively new and have only been inproduction and available for general use for a relatively short time.Direct view storage tubes provide a continuous visual representation ofa nonrepetitive electric signal. These tubes are particularly wellsuited for displaying radar and processed alpha numeric information. Theexterior of the tube resembles very closely ordinary cathode ray andtelevision picture tubes and are manufactured in various sizes rangingfrom to 21" in diameter.

There are basically two types of direct view storage tubes and they areidentified as bi-stable and half-tone. The bi-stable type provides ablack and white picture having two shades and incorporates regenerativecircuits to provide a long retention time. The half-tone type, withwhich this invention is primarily concerned, is ca pable of providing acontinuous range of shades of gray, but has a finite retention time. Thephysical structure, both internal and extrenal, of the two is similarand the difference in operation is the result of the operatingtechniques.

When the storage tube is operated as a half-tone type, it is necessaryto periodically and cyclicly erase the image and the background forbrief predetermined periods of time. It has been found from experiencethat the image will decay rapidly with these erase pulses down to acertain intensity but thereafter the decay of the image with theapplication of additional erase pulses is very slow. This factorpresents an obstacle when the tube is used for displaying moving targetssuch as radar type display or when presenting rapidly changing alphanumeric displays. The faint images may be completely erased byincreasing the length of time of the erase pulse while holding itscyclic repetition rate constant. However, this results in the completeerasure of the wanted images also, since the extended erase pulseaffects both the faint images and the desired information equally.

One object of this invention is to provide a methodof operating a directview storage tube such that a uniform decay of the charge over theentire dielectric storage surface is obtained.

Another object of the invention is to provide means of implementing auniform decay of the electric charge over the entire dielectric surfaceof a direct view storage tube.

A further object of the invention is to provide means for uniformly andlinearly erasing the image displayed on a direct view storage tube.

In the drawings:

FIGURE 1 is a schematic view of tube;

FIGURE 2 is a cross-sectional view of a portion of the storage surfaceshown in FIGURE 1;

FIGURE 3 is an isometric schematic view of the electron writing gunshown in FIGURE 1;

. FIGURE 4 is a schematic diagram illustrating the basic manualoperation of the storage tube according to the invention; and,

FIGURE 5 is a schematic and block diagram of a novel control circuitconstructed according to the invention.

a direct view storage In FIGURE 1, the picture tube shown may beconstructed similar to the direct view storage tube marketed by theHughes Aircraft Corp. of Culver City, California, under the trade nameTypotron. This tube is described in technical memorandums No. 496 andNo. 511 published August 1957 and May 1958, respectively, by the abovesaid Hughes Aircraft Corp. Tubes of this type are also described in thefollowing publications; proceed ing of the IRE, volume 41, pages 1167 to1171, published September 1953; proceeding of the IRE, volume 42, pages1496 to 1504, published October 1954, and the IRE Wescon ConventionRecord, volume 1, part 7, page 78, published in 1957.

The tube shown in FIGURE 1 has an envelope 1 which is shaped generallylike a television picture tube. The narrow neck portion 3 contains anelectron Writing gun 4 which will be described in detail later inconnection with the description of FIGURE 3. An electron flood gun 5 ispositioned at the back end of the tube near the writing gun 4 andprovides a supply of relatively low energy electrons directed towardsthe face 6 of the tube 1. The electrons are collimated by a collimatingelectrode 8 which is annular in shape and is positioned adjacent to thebell portion 9 of tube 1. Collimating electrode 8 is connected to aterminal 11 and is energized in a manner which will be described later.The face 6 of tube 1 has a conductive phosphor 12 deposited on its innersurface, which is connected to a terminal 13 for energization in amanner which will be described later. Two mesh type electrodes 15 and 20are located adjacent the phosphor surface 12. The storage surface meshelectrode 15 is located adjacent surface 12 and has a dielectricmaterial 17 deposited on that side of the mesh which faces flood gun 5.Mesh electrode 15 is connected to a terminal 19 for energization in amanner which will be described later. The collector mesh 20 is spacedfrom but located adjacent the dielectric material 17 and is connected toa terminal 21 for energization. Here again, how the energization takesplace will be described later.

FIGURE 2 shows a fragmentary portion of mesh 15 and dielectric material17 in cross section which illustrates how the dielectric materialextends and envelops three sides of the mesh 15 so that portions of thedielectric material are in the shadow of the flood gun electrons andface the phosphor 12.

In operation, terminal 13 is connected to a high potential positivedirect current source having a voltage somewhere between +6 and +10 kv.The storage mesh via terminal 19 is placed at a relatively low positivedirect current potential which may be of the order of magnitude of +12volts. The collector mesh 20, via terminal 21, is connected to anotherpositive direct current source which may have an order of magnitude ofapproximately volts. The collimating electrode 8, via terminal 11, isconnected to a positive voltage source which may be somewhere around 40volts. The voltages stated above are not critical and may be varied fordifferent operating characteristics.

When the tube is connected to the voltage sources, the dielectricmaterial 17 will be negatively charged which with the above voltageswill be about 3 volts when erase pulses which will be described laterare applied to grid 15, thus the electrons from the flood gun 5 which isoperated at zero cathode potential will not reach the dielectric 17 butwill be collected by electrode 20; nor may they pass the storage mesh 15to energize the phosphor 12. However, when the writing gun 4 isenergized and high energy electrons from the gun are directed to a givenarea on the storage electrode 15 they positively charge the dielectric17 which is deposited on that area i by secondary emission andthereafter those flood gun electrons directed to that area will passthrough the storage mesh. The flood gun electrons which pass through themesh in the area charged by the writing gun electrons are thenaccelerated towards the phosphor 12 to energize the phosphor on impact.

Unfortunately, the charge pattern established by the writing gun 4 isaltered during operation by the positive ions formed by the interactionof the flood gun electrons and the residual gas in the tube envelope.These ions are attracted toward the negative portions of the storageelectrode and slowly charge it in the positive direction. Thus, in theabsence of corrective action, the background of the display is raised toa light intensity level comparable to the light intensity level of thedisplayed information which results in a gradual washout of theinformation displayed on the phosphor. Depending on the operatingvoltages used, a complete washout may take as long as five minutes.

The washout effect caused by the deposited ions, may to a certainextent, be overcome by a controlled cyclic erasing process which isknown in the art. The erasing process is effected by applying a positivesquare wave voltage to terminal 19. For the voltages set forth above,the square wave voltage would be approximately +3 volts. This voltageraises the potential of the storage surface by that amount. If a portionof the surface is at -3 volts which is cutoff, it is elevated to groundpotential where it will remain regardless of the length of the pulse.When the pulse is removed, that portion of the storage surface willreturn to cutoff 3 volts. However, those areas which have, prior to theapplication of the erase pulse, risen to a higher voltage than 3 voltsdue to ion action will be elevated to some positive voltage above thepotential of the flood gun and the flood electrons will lower thevoltage of that portion of the storage surface at a rate which isdetermined by the dielectric material. If the pulse persists for arelatively long period of time, the potential of that area will decreaseto the cathode potential of the flood gun, and will further decrease to3 volts when the pulse is removed. This results in a complete erasuresince -3 volts is cutoff. However, a long pulse will also result in acomplete erasure of the written material. Therefore, short pulses areapplied at a relatively low frequency of the order of magnitude of 60cycles. The length of these pulses or the duty cycle is selected so thatthe information on the storage surface electrode of the tube decays at aslow rate.

Unfortunately, the decay of the information is not linear. The initialdecay is linear to a predetermined relatively low, but nevertheless,visible intensity. Thereafter it changes its rate of decay very slowlyand remains visible but faint. Such a tube decay characteristic isundesirable when displaying the output of a radar tracking device orrapidly changing alpha numeric information. A uniform decay all the waydown to zero intensity of the display with respect to time is necessaryfor the proper operation of the tube.

If the phosphor potential, which is between +6 to +10 kv., is reduced tol volts, or some other comparable minus potential during the erasepulse, it has been found that the decay characteristics of the image aresubstantially linear from the highest to zero intensity which providesoperating characteristics highly suitable for displaying radar trackinginformation and rapidly changing alpha numeric information.

It is believed that the dielectric surface 17 is not uniformlydischarged by the flood gun electrons when the phosphor surface is atthe normal operating voltage of between +6 and +10 kv. Referring toFIGURE 2 which shows an enlarged detail of the mesh and the dielectriccoating, one ean see that the portions of dielectric material 17adjacent to the openings in the mesh 15 are in the shadow of the floodelectron beam and, therefore, are least effected by the electrons in thebeam. Furthermore, when the electrons reach the hole area in thedielectric, they are then influenced by the high voltage on the phosphorand are accelerated towards the phosphor and fail to discharge thedielectric surface in the hole area. However, when the high positivevoltage on the phosphor is removed and a negative voltage substituted,the flood electrons which reach the hole area are no longer acceleratedtowards the phosphor but are returned or reflected back toward thedielectric to more effectively discharge those portions of thedielectric material which are in the shadow of the flood gun electronbeam. This action, it is believed, provides a uniform decay of thecharge on the dielectric surface over its entire area, thus providing alinear erase Without the need of an overly long erase pulse which woulderase the written information too rapidly.

The writing gun shown in FIGURE 3 has a source of high energy electrons30 immediately followed by a pair of horizontal deflection plates 31 anda pair of vertical deflection plates 32. The vertical deflection plates32 are followed by an extrusion die 34 which bears the various alphanumeric characters. The beam of electrons from source 30 is positionedon the correct alpha numeric character on extrusion die 34 by horizontaland vertical deflection plates 31 and 32, respectively. The extrudedbeam emerging from matrix 34 is centered by a magnetic convergence coil36, and two pairs of vertical and horizontal compensating plates 37 and38, restore the extruded beam to the axis of the writing gun. Followingthe compensating plates are additional pairs of vertical and horizontaldeflection plates 39 and 40, respectively, which deflect the extrudedwriting beam to the desired display position on the face of the tube.

When a particular character is desired, its xy coordinates on matrix 34are applied in the form of electric signals to plates 31 and 32,respectively. This deflects the writing beam to the correct characterposition on matrix 34. Convergence coil 36 and compensating plates 37and 38 restore the extruding beams to the axis of source 30 and electricsignals representing the x-y coordinates on the face of the tube wherethe character is to be displayed are applied to deflection plates 40 and39, respectively.

FIGURE 4 illustrates how the invention may be practiced manually. Thephosphor 12 is connected via terminal 13 and a single pole double-throwswitch 41 alternately to a positive voltage source having a voltagebetween +6 and +10 kv. and a negative source of voltage; and storagegrid 15 is connected via terminal 19 and another single poledouble-throw switch 42 alternately to a source of positive voltage whichmay be +12 volts and another positive source of voltage which may be +15volts. Switches 41 and 42 are ganged and will operate simultaneously. Anoperator may, at selected intervals, move the switches 41 and 42 fromthe position shown in the drawing to the alternate position for apredetermined time and then restore them to the position illustrated.When the switches are in the position illustrated, the phosphor isconneced to the high positive voltage and the storage grid is connectedto the operating bias voltage. When both switches are moved to thealternate position, a +3 volt square wave is applied to the storage gridand the phosphor is simultaneously connected to the negative voltagesource which in conjunction with the positive square wave provides theuniform erasure of the entire dielectric surface on the storage grid.

In FIGURE 5 an alternating current is applied to a blocking oscillator50. The frequency of the alternating current establishes the repetitionrate of the pulses applied to the storage mesh 15. Blocking oscillatorhas its output applied through a delay multivibrator 51 to aconventional multivibrator 52 and the output of multivibrator 52 is thenconnected to storage mesh 15 by conductor 53.

Blocking oscillator 50 also has its output applied to the set input of aflip-flop 55. The output of multivibrator 52 is differentiated in adifferentiating circuit 56 and its output has the positive peaks clippedin a clipping circuit 57 and the output of clipping circuit 57 isapplied to the reset input of flip flop 55. Thus, flip flop 55 providesa suitable output when set and this output is extinguished when the flipflop is reset. The output on conductor 53, which is applied to thestorage mesh grid will, in the specific embodiment chosen forillustration with the values set forth above, provide a positive goingpulse of 3 volts peak-to-peak amplitude at a +12 volt D.C. level ofpredetermined width at a 60 cycle repetition rate when the inputconnected to blocking oscillator 50 alternates at 60 cycles.

A free running multivibrator oscillator 59 is connected to a low voltagepower supply and has its output connected through a pulse shaper circuit60 and a regulator 61 to a flyback high voltage generator 63. The outputof generator 63 is connected to the phosphor 12 by a conductor 64. It isalso fed back to regulator 61 by a voltage divider network comprising apair of resistors 65 and 66 connected in series between the output ofgenerator 63 and a negative voltage source connected to a terminal 67.In addition the output of generator 63 is also connected to the plate 69of a shunt triode vacuum tube 70 which has its cathode 71 connected to asecond negative voltage supply by a terminal 72. The output of flip flop55 previously described is connected to the grid 74 of tube 70 and tothe common junction of resistors 65 and 66 by a diode 76. When theoutput of flip-flop 55 is in the reset condition, that is negative,shunt tube 70 is open circuited and the output of generator 63, exceptfor that portion fed back to regulator 61, is applied to the phosphor12. However, when flip flop 55 is in the set condition and its output ispositive, shunt tube 70 conducts and reduces the voltage at the outputof generator 63 which is available to the phosphor to some negativevalue which is determined by the voltage applied to terminal 72. Ifterminal 72 is connected to a -300 volt supply, the voltage applied tothe phosphor 12 will be approximately 125 volts when the output of flipflop 55 is positive. At the same time, the positive voltage from flipflop 55 is applied through diode 76 to inhibit regulation during thismode of operation. When the flip flop is reset and the output becomesnegative, diode 76 opens and normal regulation takes place. In theembodiment chosen, high voltage generator 63 is operated so as toprovide a +9 kv. output and the wave forms of the outputs on conductors53 and 64 are graphically illustrated. The pulse on conductor 53 isdelayed by delay multivibrator 51 so as to permit sulficient time forthe voltage on conductor 64 to decrease to the 125 volt level before theerase pulse on conductor 53 is applied to the storage mesh grid 15.

While only one embodiment of the invention has been shown and describedin detail for illustration purposes, it is to be undersood that theinvention is not to be limited thereto.

What is claimed is:

1. A circuit for controlling theerasure of a direct view storage tubewhich includes a storage surface electrode and a phosphor screen, saidcircuit comprising first means for supplying electric signals at apredetermined frequency, delay means actuated by said first means forsupplying pulsed electrical energy at the frequency of the first meansbut delayed in time, second means for connecting said delayed pulses tothe storage surface electrode, third means for supplying a regulatedhigh voltage connected to said phosphor screen, and fourth meansresponsive to the said first means and said delay means for periodicallyreducing the voltage from the regulated power supply to a predeterminednegative value and restoring it to the initial value at the terminationof the pulse applied to storage surface electrode,

2. A circuit for controlling the erasure of a direct view storage tubewhich includes astorage surface electrode and a phosphor viewing screen,said circuit comprising a blocking oscillator connected to a source ofalternating voltage for supplying pulsed electric energy, a delaymultivibrator connected to said blocking oscillator for supplying pulsedelectrical energy having the same frequency as the frequency of saidblocking oscillator but delayed in time, a multivibrator connected toand responsive to said delay multivibrator for supplying, electricpulses of the same frequency as said multivibrator but having apredetermined minimum and maximum voltage and duty cycle, to the storagesurface electrode, an oscillator circuit connected to a low voltagepower supply for supplying high frequency electric energy, a pulseshaping circuit connected to said oscillator for providing a steppedsaw-tooth wave having the same frequency as the oscillator outputfrequency, a voltage regulator circuit connecting said pulse shapingoutput to a high voltage generator the output of which is connected tothe phosphor viewing screen, a voltage dividing network connected to theoutput of the high voltage generator for feeding back a portion of theoutput to the regulating means to prevent high voltage fluctuations, aflip flop having one input connected to the output of the blockingoscillator to provide an output when said blocking oscillator energizesthat input and its other input connected to the output of themultivibrator by means which provide a pulse at the trailing edge of themultivibrator output which deenergizes the flip flop, means connected tothe output of the high voltage generator and operated by the output fromthe said flip flop when the said input is energized by the blockingoscillator for reducing the output voltage of the generator to apredetermined negative voltage level, and asymmetric conducting meansconnected by the said flip flop output and the regulator for disablingsaid regulator during those periods when the flip flop provides anoutput.

3. A circuit for controlling the erasure of a direct view storage tubewhich includes a storage surface electrode and a phosphor viewingscreen, said circuit comprising a source of pulsed electric energy, afirst multivibrator responsive to said source for supplying pulses ofelectric energy having the same frequency as the frequency of saidsource but delayed in time, a second multivibrator connected to andresponsive to the first multivibrator for energizing the storage surfaceelectrode, a high voltage generator connected to a source of highfrequency electric energy for supplying a high positive operatingvoltage to the phosphor viewing screen, a flip flop having one inputconnected to the source of pulsed electric energy to provide an outputwhen said source energizes that input and its other input connected tothe output of the second multivibrator by circuit means for providingpulses coinciding with the trailing edges of the second multivibratoroutput to de-energize the flip flop, and means connected to the outputof the high voltage generator and operated by the output from the flipflop when the flip flop input is energized by the source of pulsedelectric energy for reducing the output voltage of the high voltagegenerator to a predetermined negative voltage level.

4. A circuit for providing a substantially linear erasure of a directview storage tube which includues an energized storage surfaceelectrode, a flood gun and an energized phosphor screen, said circuitcomprising, means for periodically applying an erase pulse to thestorage surface electrode, and means operative simultaneously andcoextensively with the said first means for accelerating the electronssupplied by the flood gun toward the rear surface of the storage surfaceelectrode comprising means for reducing the potential of the energizedphosphor viewing screen to a predetermined voltage which is below thevoltage of the flood electrons supplied by the flood gun for theduration of the said erase pulse.

5. A circuit for providing a substantially linear erasure of a directview storage tube which includes an energized storage surface electrode,an electron flood gun and an energized phosphor screen, said circuitcomprising, means for applying a periodic positive erase pulse to thestorage surface electrode, and means operative simultaneously andcoextensively with said first means for accelerating the electrons fromthe flood gun toward the rear surface of the storage surface electrodecomprising means for reducing the high positive potential on thephosphor viewing screen to a predetermined negative voltage which isbelow the voltage of the flood electrons supplied by the said flood gunfor the duration of the said erase pulse.

6. A circuit for providing a substantially linear erasure of a directview storage tube which includes an energized storage surface electrode,an electron flood gun and an energized phosphor screen, said circuitcomprising, means for periodically reducing the potential on thephosphor viewing screen to a predetermined voltage which issubstantially below the potential of the flood gun electrons foraccelerating the flood electrons towards the rear surface of the storagesurface electrode, means for applying an erase pulse of a predeterminedlength to the storage surface electrode of the tube when the saidphosphor viewing screen potential reaches the said predeterminedvoltage, and means for restoring the viewing screen potential at thetermination of the erase pulse applied to the storage surface electrode.

7. A circuit for providing a substantially linear erasure of a directview storage tube which includes an energized storage surface electrode,an electron flood gun and an energized phosphor screen, said circuitcomprising, means for periodically reducing the potential on thephosphor viewing screen to a predetermined negative voltage which issubstantially below the potential of the flood gun electrons foraccelerating the flood gun electrons towards the rear surface of thestorage surface electrode, means for applying an erase pulse of apredetermined length to the storage surface electrode of the tube whensaid phosphor viewing screen attains the said predetermined negativevoltage, and means for returning said viewing screen to its initialpotential at the termination of the said erase pulse.

References Cited in the file of this patent UNITED STATES PATENTS2,873,404 Stone Feb. 10, 1959 2,967,969 Stocker Jan. 10, 1961

1. A CIRCUIT FOR CONTROLLING THE ERASURE OF A DIRECT VIEW STORAGE TUBEWHICH INCLUDES A STORAGE SURFACE ELECTRODE AND A PHOSPHOR SCREEN, SAIDCIRCUIT COMPRISING FIRST MEANS FOR SUPPLYING ELECTRIC SIGNALS AT APREDETERMINED FREQUENCY, DELAY MEANS ACTUATED BY SAID FIRST MEANS FORSUPPLYING PULSED ELECTRICAL ENERGY AT THE FREQUENCY OF THE FIRST MEANSBUT DELAYED IN TIME, SECOND MEANS FOR CONNECTING SAID DELAYED PULSES TOTHE STORAGE SURFACE ELECTRODE, THIRD MEANS FOR SUPPLYING A REGULATEDHIGH VOLTAGE CONNECTED TO SAID PHOSPHOR SCREEN, AND FOURTH MEANSRESPONSIVE TO THE SAID FIRST MEANS AND SAID DELAY MEANS FOR PERIODICALLYREDUCING THE VOLTAGE FROM THE REGULATED POWER SUPPLY TO A PREDETERMINEDNEGATIVE VALUE AND RESTORING IT TO THE INITIAL VALUE AT THE TERMINATIONOF THE PULSE APPLIED TO STORAGE SURFACE ELECTRODE.